Genyzme Genetics, the national laboratory owned by Genzyme, has launched population carrier and prenatal diagnostic testing for spinal muscular atrophy (SMA), the most common inherited cause of infant mortality.

An autosomal recessive disease, SMA is characterized by progressive muscle degeneration of motor neurons, resulting in severe muscle weakness. In 60-70 percent of cases, children with SMA die from respiratory failure by age two. After cystic fibrosis, SMA is the second most common lethal autosomal recessive disease in the United States.

To test for SMA, Genzyme licensed from Athena Diagnostics (owned by Thermo Fischer) a quantitative polymerase chain reaction (PCR)-based assay that can determine the number of SMN1 genes. An individual with one SMN1 gene is a carrier of SMA; a fetus with no SMN1 genes will be affected with SMA. SMA is caused when both parents have only one SMN1 gene. Approximately one in 41 people is a carrier of the SMA-causing gene, resulting in an incidence rate of 1 in 6,000-10,000 births. If both parents are found to be carriers, prenatal diagnosis by chorionic villi sampling or amniocentesis is available.

"Carriers of SMA have no symptoms of the disease and rarely have a family history of SMA," says Stirling M. Puck, M.D., of Genzyme Genetics. "Advancements in technology have led to the ability to detect approximately 94 percent of carriers, and then to offer prenatal testing to at-risk parents; these advancements will help couples planning a pregnancy make informed decisions." Greater than 94% of SMA carriers have a deletion of one SMN1 gene.